1. Field of the Invention
The present invention relates generally to x-ray systems and devices. More particularly, embodiments of the invention concern an x-ray device shield structure and focal spot control assembly that contributes to improved x-ray device performance, through enhanced heat management within the x-ray device and by way of focal spot control.
2. Related Technology
X-ray systems and devices are valuable tools that are used in a wide variety of applications, both industrial and medical. For example, such equipment is commonly used in areas such as diagnostic and therapeutic radiology, semiconductor manufacture and fabrication, and materials analysis and testing.
While used in a number of different applications, the basic operation of x-ray devices is similar. In general, x-rays are produced when electrons are produced and released, accelerated, and then stopped abruptly. A typical x-ray device includes an x-ray tube having a vacuum enclosure collectively defined by a cathode cylinder and an anode housing. An electron generator, such as a cathode, is disposed within the cathode cylinder and includes a filament that is connected to an electrical power source such that the supply of electrical power to the filament causes the filament to generate electrons by the process of thermionic emission. The anode is disposed in the anode housing in a spaced apart arrangement with respect to the cathode. The anode includes a target surface, sometimes referred to as a “target track” or “focal track,” oriented to receive electrons emitted by the cathode. Typically, the target surface is composed of a material having a relatively high atomic number, such as tungsten, so that a portion of the kinetic energy of the striking electron stream is converted to electromagnetic waves of very high frequency, namely, x-rays.
In operation, the electrons are rapidly accelerated from the cathode to the anode under the influence of a high electric potential between the cathode and the anode that is created in connection with a suitable voltage source. The accelerating electrons then strike the target surface at a high velocity. The resulting x-rays emanate from the target surface, and are then collimated through a window formed in the x-ray device for penetration into an object, such as the body of a patient. The x-rays that pass through the object can then be detected and analyzed so as to be used in any one of a number of applications, such as x-ray medical diagnostic examination or material analysis procedures.
A relatively large percentage of the electrons that strike target surface of the anode do not cause the generation of x-rays however and, instead, simply rebound from the target surface. Such electrons are sometimes referred to as “back-scatter” or “rebound” electrons. In some x-ray tubes, some of these rebounding electrons are blocked and collected by an electron collector that is positioned between the cathode and the anode so that rebounding electrons do not re-strike the target surface of the anode. In general, the electron collector thus prevents the rebounding electrons from re-impacting the target anode and producing “off-focus” x-rays, which can negatively affect the quality of the x-ray image.
Typically, such electron collectors define an aperture through which the emitted electrons pass from the cathode to the target surface of the anode. To this end, the aperture includes or defines an inlet positioned near the cathode, as well as an outlet positioned near the target surface of the anode. In at least one implementation, the aperture is configured so that the inlet has a diameter that is relatively larger than the diameter of the outlet.
While such electron collectors have proven useful in some applications, some problems nonetheless remain. For example, the geometry of some electron collectors is such that the electron collector experiences undesirable heat concentrations. Such heat concentrations can cause, among other things, thermal stress and strain that may ultimately contribute to structural failure of the collector. More particularly, non-uniform thermal expansion of structural elements, such as is produced by high temperature differentials, induces destructive mechanical stresses and strains that can ultimately cause a mechanical failure in the part.
Yet other concerns with some typical electron collectors relate to the heat flux distribution associated with the electron collector. In particular, the heat flux distribution within typical electron collectors is generally non-uniform. As a result, such electron collectors are prone to heat concentrations that impose harmful, and potentially destructive, thermally-induced stresses and strains on the electron collector, as well as on other components of the x-ray device. Further, such heat concentrations tend to diminish the efficiency and effectiveness with which heat can be removed from typical electron collectors.
Finally, x-ray devices that incorporate or include an electron collector typically lack devices or systems that are effective in guiding an electron beam through the electron collector and/or adjusting the position of the focal spot on the target track of the anode. Consequently, the tomographic, and other, information that can be obtained in connection with such fixed focal spot type devices is somewhat limited. Moreover, the target track of the anode may experience premature wear and failure as a result of the continued presence of the focal spot at the same location on the target track.
In view of the foregoing, and other, problems in the art, what is needed is a shield structure and focal spot control assembly that includes a shield structure configured and arranged such that heat flux distribution is substantially uniform throughout the interior surface of the shield structure. Additionally, the shield structure and focal spot control assembly should incorporate systems and devices that enable control of the location of the focal spot.